An image forming apparatus such as a printer is conventionally provided with a carriage which is reciprocable in a direction perpendicular to a paper feed direction (a main scanning direction) by a driving force transmitted from a stepping motor or a DC motor with an encoder through a train of gears.
During printing, the carriage selectively ejects ink from ink jet nozzles formed at the lower face of the carriage on the basis of dot pattern data while reciprocating.
Although the control of the reciprocation of the carriage is performed by controlling the rotation amount of the stepping motor or the DC motor with an encoder as the driving source, the control cannot be achieved in a highly accurate manner because of rotational pitch errors due to the structure of the motor, accuracy errors of gears caused during manufacture thereof or the like.
Regarding paper feed, although the control of the feed amount of paper is performed also by controlling the rotation amount of the stepping motor or the DC motor with an encoder as the driving source, the paper feed cannot be achieved in a highly accurate manner because of rotational pitch errors due to the structure of the motor, accuracy errors of gears caused during manufacture thereof, errors in outer diameters of feed rollers, errors in feed amounts that are dependent on the types of paper used, or the like.
There are further problems that when the actual paper feed direction is deviated with respect to the feed path of the printer, the printing area of paper is shifted from the center, and that when paper of a different type from that of the paper set at the printer is supplied, requirements for printing become inappropriate and thus printing cannot be performed appropriately.